1. Field of the Invention
The present invention relates to head up display systems, more particularly to a head up display and vision system which displays a real time, high resolution integrated computer and video image.
2. Prior Art
An operator of a vehicle such as an aircraft, ship, train, truck or the like conventionally must view the scene in front of the vehicle based on the visible light available, either natural or artificial, to determine whether it is safe to advance the vehicle. The operator's vision can be obscured by clouds, fog, smoke or various forms of precipitation such as rain, sleet and snow as well as man-made obstructions. These conditions distort the operator's view of the landing strip for an aircraft, the harbor for a ship, train tracks for an engine or roadways for trucks or other wheeled vehicles. The operator's viewing difficulties are compounded at night when natural visible light is absent and the operator must rely upon artificial light such as runway lights to determine whether the vehicle is moving in the correct direction and at the proper speed and/or altitude. Such artificial lights are particularly subject to distortion or obstruction by inclement weather.
Attempts have been made to improve the information provided to the operator of a vehicle by use of a transportation guidance system. For example, certain aircraft have been equipped with a flight guidance system known as a head up display (HUD). A HUD projects a synthetic representation of the runway or other scene on an optical combiner positioned directly in front of the pilot's head. The pilot's head need not be moved to look down at the cockpit dials. The runway or other scene is projected on the HUD along with other information on the aircraft's speed and position, thus the pilot need not actually directly see the runway. An aircraft HUD may incorporate various flight location and performance information including altitude, glide slope angle, speed and the like to provide the pilot with an image of the runway as it appears from the approaching aircraft. This type of aircraft guidance system merely incorporates navigational data into an image of the runway but does not produce an image of the runway scene.
A HUD imaging system disclosed in U.S. Pat. No. 5,534,694 represents an attempt to provide an actual image of the scene in front of an aircraft. The system uses an infrared imaging sensor which detects radiation emanating from objects in a runway scene outside the range of visible light. Each object in the scene has a characteristic spectral signature which may be detected by a radiation sensor. In that system, the infrared sensor detects wavelengths of infrared radiation having wavelengths of 1 to 5 .mu.m. A wavelength attenuator selects one set of wavelengths of 1 to 3 .mu.m containing radiation from runway lights and another set of wavelengths of 3 to 5 .mu.m containing radiation from objects in the runway scene. A signal processor combines the two sets of wavelengths and produces an image based on the infrared radiation detected. The infrared image is superimposed upon the operator's direct visual view of the runway scene. The optical system used in this system detects radiation in the 1 to 5 .mu.m range and thus is limited in its ability to detect other types of radiation emanating from various structures present on the runway scene.
A need remains for an imaging system which detects and incorporates radiation emanating from a scene in the ultraviolet through infrared radiation wavelengths of the electromagnetic spectrum that is selected by the operator for existing operating conditions and immediate mission objectives.